Subject: Re. Cowbirds and RW Blackbirds
Date: Aug 26 00:32:33 1997
From: Jack Bowling - jcbowling at mindlink.bc.ca


Michael Price wrote: >. At Iona this summer I observed
a female Red-winged Blackbird, an unlikely host
species, feeding a juv cowbird at the Iona
settling ponds >

then Chris Maack wrote: >
Michael, in researching brown-headed cowbirds for an
educational presentation, I learned that red-winged
blackbirds are quite regularly parasitized by cowbirds.
The interesting thing is that they are among the few
species that would be physically able to eject
cowbird eggs without puncturing them (thereby
messing up the nest), but do not choose to do so.
Their populations appear to be withstanding the
threat nicely also. Perhaps there is plenty of chow
to go around, or their own nestlings are more
competitive.

Perhaps only indirectly related to this topic, I recently
talked to Wayne Campbell who finished a 2nd year of field work in
northern BC this past summer. He had a theory that estimating the
number of Red-winged Blackbirds (RWBL) by counting the singing
males on the cattails and multiplying by two is fraught with
inaccuracy due to the polygamous nature of the males. Indeed, he
found one marsh where the ratio was 3:1 females to males!

I don't know if this could be worked into some kind of theory on
why RWBL are not cowbird egg rejectors, but it's worth a shot.
Essentially, the question can be posed: do polygamous species
that are cowbird hosts tend not to rejectors?

- Jack

Jack Bowling
Prince George, BC
jcbowling at mindlink.bc.ca